This invention relates to an ink jet printing apparatus wherein a printing head having a plurality of nozzles is moved relatively to a recording medium, and ink droplets are jetted selectively from the individual nozzles by the sudden reduction of the inner volume of an ink chamber communicating with the nozzles to print characters or figures.
An ink jet printing apparatus of such type is disclosed, for example, in U.S. Pat. No. 3,946,398. In such a recording system, since ink droplets are jetted selectively from the nozzles depending on a printing pattern, some of the nozzles are often left in a state waiting for ejection for a long time so that ink-failure is liable to occur not only at initiation of the printing but also during the printing operation due to the clogging of the nozzle tip.
In the meantime, there have been heretofore known several single-nozzle type ink jet printing apparatuses which may avoid a possible ink-failure problem, including the one disclosed in U.S. Pat. No. 3,925,789 in which the recording action is performed posterior to an ink-failure preventive ejection if a printing instruction is received after non-printing period exceeds a preset time of a timer; the one disclosed in Japanese Published Unexamined Patent Application No. 57518/1975 and U.S. Pat. No. 3,925,788 in which an ink-failure preventive ejection is performed at the interval of a timer preset time during the non-printing period; and the one disclosed in Japanese Published Unexamined Patent Application No. 93633/1976 in which an ink-failure preventive ejection is effected for a predetermined short period of time if the non-printing state is present during the predetermined short period at the interval of a timer preset time. Thus, the ink-failure preventive ejection in any of the known single-nozzle type ink jet printing apparatuses is carried out for the first time after occurrence of a non-printing state where print information is not fed to a print controller while a printing device is supplied with an electric power. Therefore, if the above technic is applied to a multiple-nozzle type ink jet printing apparatus, apart from ink-failure preventive ejection required at the initiation of printing, it becomes necessary to check the jetting state of each nozzle for the prevention of an ink-failure that would occur in the nozzles which are not in continuous jetting action and are in the waiting state during the printing mode, so that complication of the apparatus structure is unavoidable. In addition, it is extremely difficult to enable the nozzles, which are arrayed in parallel in the printing head, to perform selective ink-failure preventive ejection.